The present invention relates generally to fuel injection systems for internal combustion engines and relates more particularly to leakless nozzle and holder assemblies for use with multi-cylinder diesel engines.
In the conventional fuel injection nozzle and holder assembly, leakage fuel which passes along the nozzle valve into the spring chamber is removed from the holder assembly by an external leakoff harness connected to the fuel sump. Although such an arrangement requires additional external plumbing to be affixed to already overly complicated engines, the leakoff systems were considered necessary in order to prevent an unreasonable buildup of pressure within the spring chamber which could modify and interfere with the proper and predictable action of the spring in controlling the opening and closing of the nozzle valve.
Modern injection systems have been developed which either by elimination of the pump delivery valve or by other pressure relieving means provide a substantial reduction in the delivery line pressure between injection intervals. Assuming the spring chamber volume is adequate, it is possible to operate essentially conventional fuel injection nozzle and holder assemblies with such types of pumps without a separate arrangement for the removal of leakage fuel from the spring chamber. In such systems, the spring chamber fuel pressure is permitted to build up to a certain predictable level, at which it becomes stabilized and assists the spring in providing a closing force against the valve. This arrangement is particularly advantageous since the leakage fuel pressure in the spring chamber will be smaller under low speed and low load conditions when it is desirable to have a smaller nozzle opening force.
A potential difficulty with the described arrangement is the sealing of the spring chamber by the engagement of the valve with the valve stop means during the injection interval which prevents leakage fuel from penetrating into the spring chamber during injection. If such sealing should occur, the spring chamber fuel pressure in that particular nozzle will be lower than that of the other engine nozzles and the nozzle valve opening and closing pressure will accordingly be different, resulting in a non-uniform fuel delivery to the engine cylinders. By the arrangement of the present invention, the sealing of the spring chamber is no longer a potential problem and the spring chamber pressures will be predictable and uniform for each of the nozzle and holder assemblies of the engine.